13th Conference on Mountain Meteorology

2.3

Mediterranean Lee Cyclogenesis

Ron McTaggart-Cowan, MSC, Montreal, QC, Canada; and T. J. Galarneau and L. F. Bosart

This study investigates the formation and intensification of a

rapidly-developing cyclone that formed in the Gulf of Genoa on 15

November 2007. This region has been shown to be

climatologically active in terms of lee cyclogenesis; however studies

investigating Gulf of Genoa development

focus almost entirely on the role of the Alps in the dynamics of the

cyclgenetic process.

The symmetric, spiral nature of the mature system, combined with

satellite observations that suggest the presence of a deep warm core

at its centre, leads to the hypothesis that the November 15 cyclone

(whose near-surface winds reached 50 kt) extracted and converted

significant energy from the warm underlying Mediterranean waters in

the form of latent heat fluxes and deep moist convection. These

processes have been shown to be fundamentally important for the

formation of both

Mediterranean hurricanes and polar lows, both of which are

structurally similar to the "lee cyclone" studied here.

In order to identify the cyclogenetic mechanisms fundamental to this

case, a modelling study has been undertaken using the Canadian

Meteorological Centre's Mesoscale Alpine Project (MAP D-PHASE) domain,

run operationally over this period in support of the D-PHASE

operational period. Using time-varying orography to reduce shock wave

generation, a series of tests involving the removal of flow-modifying

terrain (the Alps, the Massif Centrale, the Pyrenees, the Appenines,

and the islands of Sardinia and Corsica) are preformed. The intensity

and location of the resulting cyclone is not dramatically affected by

these extreme changes to the local orography, but the structure of the

system appears to depend on the presence of the mountain ranges.

Combining the current theories of lee cyclogenesis, polar lows and

mediterranean hurricanes, this study demonstrates that the November 15

case of lee cyclogenesis is significantly influenced by the presence

of warm Mediterranean waters beneath the cold northerly flow behind

the trough. The resulting hybrid storm is baroclinically

driven, but its intensity enhanced by the developed of reduced

convective

stability over the Gulf of Genoa.

wrf recording  Recorded presentation

Session 2, Weather Forecasting II
Monday, 11 August 2008, 10:30 AM-12:00 PM, Rainbow Theatre

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